The present invention relates to a fuel cell stack housing.
Fuel cells allow a hydrogen-containing fuel gas and an oxygen-containing reactant gas such as air to electrochemically react with each other, so that electric power is produced. The fuel cell is basically structured with a membrane that selectively transports hydrogen ions and is sandwiched between two electrodes, i.e. an anode and a cathode. The assembly of membrane and the electrodes is usually referred to as membrane electrode assembly (“MEA”). A fuel cell stack usually comprises a plurality of stacked membrane electrode assemblies, which are separated by bipolar plates.
The bipolar plates are electrically conductive separators for mechanically clamping the MEA, and for establishing electrical connection in series between adjacent MEAs. Each bipolar plate comprises a plurality of gas flow channels for supplying the corresponding electrode with the fuel gas and the reactant gas, and is further adapted to carry away generated water or excess gas. A structure body in which the MEAs are clamped between the bipolar plates is referred to as the unit fuel cell.
At both ends of the fuel call stack, the bipolar plates are formed as endplates, which clamp the fuel cell stack. For maintaining the stacked configuration and the for preventing leakage between the unit fuel cells, a preferably uniform compression force is applied to the fuel cell stack, which is adapted to press the unit fuel cells together. For maintaining the compression, fasteners such as metal bands or bolts are provided, or the fuel cell stack is accommodated in a housing. Whereas bands and housings encase the fuel cell stack, bolts interact with the endplates and hold the unit fuel cells in place.
The disadvantages of the known assemblies are various. In case the fuel cell stack is fastened by bolts, the endplates are provided with bolt holes and need to provide a sufficient strength for maintaining the compression force. This in turn results in locally varying stresses in the fuel cell stack, which may damage the fuel cell stack. The same applies for the metal bands, which are also unsuitable for providing a homogenous stress in the fuel cell stack.
For avoiding the negative aspects of the bolt holes or metal bands, it has also been proposed, to use housings which accommodate the fuel cell stack as such. However this approach leads to another problem, as the proposed housings are one-size only. The fuel cells stack, however differs in its size due to the stacked configuration of unit fuel cells. Therefore, also the stress applied to the fuel cell stack in the one-size housing varies. This may even result in situations, in which the fuel cell stack suffers from leakage (insufficient stress or in which the fuel cell stack is damaged (excessive stress).
It is desirable to provide a housing for accommodating a fuel cell stack, which provides a uniformly distributed stress in the fuel cells stack, without damaging parts of the fuel cell stack.
In the following a fuel cell stack housing comprising at least a bottom section and a first and a second side wall, which are spaced apart by the bottom section, is disclosed. The housing is further adapted to encase a fuel cell stack and comprises at least one fastening element, which is engaged with the first and the second side wall. Further at least the first side wall of the housing has a flat section and an arched section, wherein the arched section extends in direction of the second side wall. Thereby, a maximum possible distance between the arched section and the bottom section defines an inner height of the fuel cell stack housing. For providing an accommodation of the fuel cell stack which maintains a uniform applicable compression of the fuel cell stack, even if the overall size of the fuel cells varies due to its composition from the plurality of unit fuel cells, the inner height is adjustable. The height adjustment allows for an accommodation of the fuel cells, which may be adapted to the varying dimensions of the fuel cell stack. Thereby, the fuel cell stack may be accommodated in the housing without damage due to an increased stress or without deterioration of the sealing between the unit fuel cells due to insufficient stress.
Preferably, the height adjustment is induced by a tightening level of the at least one fastening element. Thereby, the housing may be pre-manufactured as standard housing which may be adapted to the individual fuel cell stack. An individual manufacturing of the housing after having determined the required height is not necessary.
According to a further preferred embodiment, the tightening level is continuously or stepwise adjustable. This allows for a very precise adjustment to the different height requirements of the fuel cell stack, which in turn provides an optimized accommodation with optimal compression force maintenance. Hence, for example, the fastening element may have a first fastening level which provides a minimal inner height and at least a second fastening level, which provides an intermediate inner height, wherein the intermediate inner height is between the minimal inner height and the inner height in an unfastened condition.
It is further preferred if the first side wall and the second side wall have flat side sections and arched sections, wherein the arched sections extend in direction of each other but are separated from each other by a gap. It should be noted that the gap is also present if only one of the side walls has an arched section. Further, it is preferred that the at least one fastening element spans the gap between the arched sections or the arched section and the side wall, respectively. Consequently, the disclosed height adjustment may be achieved by increasing or decreasing the size of the gap between the arched sections of the housing, which may be achieved by tightening the fastening element to a greater or lesser extent.
According to a further preferred embodiment, the side walls, particularly the arched sections of the side walls, provide flange elements protruding from the housing onto which the fastening elements are attached. This allows for a convenient application of fastening elements, as for example screws or bolts to the arched section of the housing.
According to a further preferred embodiment, the flat side section and the arched section of at least one side wall are integrally formed or are permanently joined together. Thereby, the overall number of elements for the housing may be reduced, which in turn may accelerate the assembling process of the housing itself.
According to a further preferred embodiment, the bottom section is detachably coupled to the side walls. This facilitates the accommodation process of the fuel cell stack into the housing since the side walls and the fastening elements may be pre-assembled. Subsequently, the housing is loaded with the fuel cell stack in a preassembled condition and is then accomplished with the bottom section.
Preferably, the bottom section and the side walls have interlocking elements, engaging each other and fixing the bottom section to the side walls. This allows for a swift assembling process of the bottom section to the side walls.
A further aspect of the present invention relates to a fuel cell stack assembly comprising a fuel cell stack accommodated in a fuel cell stack housing as defined above. Further, the fuel cell stack comprises a first endplate and a second endplate between which a plurality of unit fuel cells is arranged. Thereby, it is preferred if the first endplate is arranged in parallel to the bottom section of the housing, and the second endplate is arrange in vicinity of the arched section/s of the side walls. It should be noted that even if the bottom section and the arched section are named as bottom and top section, the housing with the fuel cell stack may also be arranged sideways, so that the bottom and top section would be presented as sides of the fuel cell stack assembly.
It is further preferable to provide pressing plate, which is arranged between the second endplate and the at least one arched section of the side wall. Thereby, the pressure applied to the fuel cell stack is uniformly distributed to the endplate and to the unit fuel cells.
According to a further preferred embodiment, a resilient element, preferably at least one spring, is arranged between the pressing plate and the second endplate of the fuel cell stack. Also, the resilient element compensates stress inequalities.
Further a shape of the pressing plate may resemble a shape of the arched section of the side wall, which also increases the homogeneity of the stress distribution to the fuel cell stack.
Further advantages and preferred embodiments are disclosed in the claims, the description and the figures. It should be further noted that a person skilled in the an may combine the presented features otherwise than indicated without extending the scope of the invention.
In the following same a similar functioning elements are indicated with the same reference numerals.